This invention relates generally to automatic palletizers and more specifically to apparatus that is employed to sense the height of the individual pallets being fed from the pallet magazine to the loading point and automatically adjusts the height of the palletizer's stripper plate to permit the pallet with or without a slip sheet to pass thereunder.
The use of pallets on which to stack products to be shipped has long been common practice in industry. The pallets are generally made from wood of varying height and have openings which permit forklifts to extend their forks through to lift the pallet and transport it between desired locations. The product or objects to be shipped are stacked or appropriately placed on top of the pallet.
Automation in manufacturing production lines has led to the development of automatic palletizers. These machines feed pallets automatically from a stack of pallets in a pallet feed rack or magazine onto a conveyor which carries the pallets to the loading point. The dispensing of the pallets along the conveyor is a stepped and timed sequence to correspond to the availability of product or material being placed upon the pallets. The product being placed upon the pallets is put there automatically in a predetermined pattern, such as by the use of a push or pull arm, or magnetic or pneumatic pick-up heads. However, in automatic palletizers the product is normally first positioned in its desired pattern on a stationary stripper plate. Once thus placed on the stripper plate, the positioned product is appropriately transferred, such as by an extendable ram or pusher, from the stripper plate onto the adjacent pallet. The loaded pallets are automatically discharged from the palletizer and then removed, generally by a forklift, to a shipping location where the product, with or without pallets, is loaded onto the appropriate means of transportation, such as a truck or railroad car.
Where pallets are used as an intermediate support for the product that is to be repackaged or moved again prior to placement on the final shipping means, slip sheets or pieces of cardboard or other material of predetermined thickness are placed on top of the pallets. The slip sheets permit a product that will be shipped without pallets to be removed more easily from the top of the pallets without damaging either the product containers or the pallets. Slip sheets also can provide the final shipping base for products when used with specially modified forklifts and unitized loads where stretch wrapping, banding, or gluing is employed. This unitized loading technique reduces the shipping freight costs and the number of costly pallets required.
Pallets present a problem in automatic palletizers, however, because of the lack of uniformity in their height. Pallets can routinely vary in height from 41/2 inches to 53/4 inches. Where slip sheets are employed, as much as an additional 1/4 inch can be added to the combined height of the pallet and slip sheet. This variation in height can cause the slip sheet to be stripped from the pallet as the pallet passes beneath the stripper plate. A greater problem however, is caused by the taller pallets which can be forced against the stationary stripper plate, causing it to flex upwardly as the pallet passes beneath. The forcing action of the pallet against the stripper plate can cause damage and excessive wear to the stripper plate, pallet, drive mechanism, or the conveyor. These and other problems are solved in the design of the apparatus comprising the present invention by employing an automatic height sensing mechanism that senses the height of the individual pallet or the slip sheeted pallet.